Molded respirator containing sorbent particles

ABSTRACT

Molded respirators containing an air-permeable, sorbent-particle-containing layer between air-permeable particle-retaining layers. The particle-containing layer is stretchable during shaping without tearing or significant loss of particles. At least some of the fibers in the particle-containing layer are sufficiently tacky after being formed by themselves into a particle-free web and cooled to room temperature so that the web will adhere to itself. The respirators can be molded from flat webs without the need to fabricate the particle-containing layer into a shaped preform.

This is a divisional of application Ser. No. 08/982,119 filed Dec. 1,1997 U.S. Pat. No. 6,102,039.

FIELD OF THE INVENTION

This invention relates to shaped fibrous respirators which can be wornto protect the wearer or surrounding personnel against air pollutantsand other airborne agents, and to processes for producing suchrespirators. This invention also relates to multilayer shapedrespirators that contain active sorbent particles in one or more of therespirator layers.

BACKGROUND OF THE INVENTION

Disposable cup-shaped multilayer fibrous respirators are described, forexample, in U.S. Pat. No. 4,536,440 (Berg), U.S. Pat. No. 4,807,619(Dyrud et al.), and U.S. Pat. No. 5,307,796 (Kronzer et al). Respiratorsfor protection against nuisance gases or vapors typically contain one ormore fibrous web layers containing sorbent particles such as activatedcarbon or alumina, and are described, for example, in U.S. Pat. No.3,971,373 (Braun), U.S. Pat. No. 4,384,577 (Huber et al.), U.S. Pat. No.4,454,881 (Huber et al.), U.S. Pat. No. 4,729,371 (Krueger et al.), andU.S. Pat. No. 4,873,972 (Magidson et al.).

Fibrous webs containing sorbent particles have been employed for avariety of other uses including vacuum cleaner bags, diapers and oilsorbents. Patents mentioning such particle-containing fibrous websinclude U.S. Pat. No. 2,988,469 (Watson), U.S. Pat. No. 3,801,400 (Vogtet al.), U.S. Pat. No. 5,149,468 (Hershelman), U.S. Pat. No. 5,486,410(Groeger et al.), U.S. Pat. No. 5,662,728 (Groeger), and InternationalApplication No. WO 97/30199 (Danaklon A/S et al.). Elastomeric orextensible webs containing particulate materials are described in U.S.Pat. No. 4,741,949 (Morman et al.), U.S. Pat. No. 5,190,812 (Joseph etal.), U.S. Pat. No. 5,238,733 (Joseph et al.), U.S. Pat. No. 5,258,220(Joseph et al.), U.S. Pat. No. 5,248,455 (Joseph et al.), and U.S. Pat.No. 5,560,878 (Dragoo et al.). Pillowed microfiber webs containingsorbent particles are described in U.S. Pat. No. 4,103,058 (Humlicek). Aparticle-laden meltblown material said to be useful for gas/vaporfiltering and/or absorbing, and specifically for disposable vacuumcleaner bags, is described in U.S. Pat. No. 4,797,318 (Brooker et al.).A particle-laden coating employing pressure-sensitive adhesivemicrofibers said to be useful for absorbent products, such as sanitarynapkins, pantyliners, incontinence products, diapers and to such relatedabsorbent products, is described in U.S. Pat. No. 5,462,538 (Korpman).

SUMMARY OF THE INVENTION

The above-mentioned U.S. Pat. No. 3,971,373 avers that particle-loadedmicrofiber sheet products may be incorporated into cup-like moldedrespirators “in the same ways as conventional non-particle-loaded webare included” (Col. 7, lines 31 et seq.). The assignee of the presentinvention has found it difficult reliably to mold respirators from websheet materials containing high particle loading levels. The particlestend to drop from the web during handling or storage, thereby leading towaste and dust formation. In addition, the molding step can cause theweb to tear or the particles to become consolidated or otherwiseredistributed within the respirator, thereby creating regions havinglower particle loading, and sometimes causing unexpectedly earlyrespirator failure.

Web tearing, and particle loss, consolidation or redistribution can bereduced by welding together two particle-containing layers along asinusoidal weld line, and then cutting and opening the resulting weldedpart to form a substantially cup-shaped preform. A similar procedureusing non-particle-containing filtration layers is described in Example22 of the above mentioned U.S. Pat. No. 4,807,619. The shape-retaininglayers of the respirator are molded in mating male and female moldhalves. The opened preform is then draped over the moldedshape-retaining layers and welded or otherwise assembled to the moldedlayers to form the finished respirator. Converting processes employingsuch a preform exhibit fewer tears, thin spots and lost particles thanconverting processes involving molding of a conventional flatparticle-containing web. However, formation of the preform requiresextra manufacturing machinery and process steps, and causes undesirablematerial waste.

The present invention provides, in one aspect, a respirator comprisingmultiple layers including an air-permeable sorbent-particle-containinglayer between air-permeable particle-retaining layers, at least one ofthe layers of such respirator being a shape-retaining layer, wherein theparticle-containing layer has a generally cup-like shape, theparticle-containing layer was stretchable during shaping to suchcup-like shape without tearing or significant loss of particles, and atleast some of the fibers in the particle-containing layer aresufficiently tacky after being formed by themselves into a particle-freeweb and cooled to room temperature so that the web will adhere toitself.

The present invention provides, in another aspect, a method for makingsuch respirators.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a respirator of the invention;

FIG. 2 is a sectional view along line 2—2 through the respirator shownin FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a particle-loaded web foruse in making respirators of the invention;

FIG. 4 is a perspective view of a particle-loaded web preform used toassemble respirators of the prior art;

FIG. 5 is an exploded perspective view of molded layers which can beused to form a respirator of the invention; and

FIG. 6 shows a pillowed web which can also be used to make respiratorsof the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, respirator 10 has a shell or respirator body 12,elastic bands 14 held in place by releasable tabs 15 of plastic or otherflexible material, a pliable dead-soft nose band 16 of a metal such asaluminum and an exhalation valve 18. Edge weld 19 holds the layers ofthe respirator together.

FIG. 2 illustrates a cross-section of the respirator of FIG. 1 takenalong line 2—2. Outer shaping layer 20 is relatively stiff and helps theparticle-containing layer maintain its cup-like shape, thereby enablingthe respirator to fit over the mouth and nose of a typical wearer.Filter layer 22 entraps airborne particles and desirably is formed froma blown microfiber web having an electret charge. Filter layer 22 isair-permeable but capable of retaining any particles (not shown) whichmay accidentally become dislodged from sorbent-particle-containing layer24. Air-permeable particle-retaining layer 26 also prevents inhalationof particles which may accidentally become dislodged from layer 24.Inner shaping layer 28 helps particle-containing layer 24 retain itscup-like shape. Outlet valve 21 permits the ready escape of air exhaledby the wearer. Facial gasket 29 improves the air seal between therespirator and the wearer's skin.

FIG. 3 illustrates a preferred particle-containing web 30 which can beused to make respirators of the invention. Web 30 is composed of sorbentparticles such as particles 33 a, 33 b, 35 a and 35 b which are adheredto one or more of fibers 32, 34 and 36. Further fibers 37 and 38 areintermeshed with the sorbent particles but not adhered to them.

FIG. 4 illustrates a typical particle-loaded web preform 40 used inprior art processes for assembling respirators. Preform halves 42 and 44are joined at curved edges 43 and 45 along weld line 46. When laid on aflat surface, preform 40 does not lie flat but instead adopts a somewhatcup-like shape. This facilitates draping preform 40 over adjacentshaping and other layers to form the completed respirator. The cup-likeshape of preform 40 enables the assembly operation to be carried outwith minimal deformation of the particle-containing layer, therebyreducing web tearing, particle loss, particle consolidation, particleredistribution or the formation of thin spots. The process of thepresent invention permits elimination of the preform fabrication stepand substitution of a generally flat particle-loaded web, therebysimplifying manufacturing and reducing material waste.

FIG. 5 illustrates several layers which can be combined to form arespirator of the invention. The layers are shown in exploded view afterthey have been molded but before they have been fastened together byedge welding and trimmed to the desired final respirator configuration.Outer shaping layer 50 has a generally smooth outer surface and can bemolded separately from the five molded layers 52, 53, 54, 56 and 58.Filtration layer 51 is fluffy and relatively formless and is drapedbetween layers 50 and 52 during manufacture. Shaping layer 52 has moldedribs 52 a, 52 b and 52 c. Charged electret filter layer 53 has moldedribs 53 a, 53 b and 53 c, traps incoming particles carried in theairstream and prevents loss of particles from particle-containing layer54. Particle-containing layer 54 has molded ribs 54 a, 54 b and 54 c.Inner particle-retaining charged electret fiber layer 56 has molded ribs56 a, 56 b and 56 c, and prevents accidental inhalation of particleswhich may become dislodged from layer 54. Inner shaping layer 58 hasmolded ribs 58 a, 58 b, and 58 c.

FIG. 6 illustrates a representative pillowed particle-containing web 60which can be used in respirators of the invention. Web 60 includespillowed low-density regions 64 surrounded by compacted high-densityregion 62. Pillowed web 60 can be formed by modifying the proceduredescribed in the above-mentioned U.S. Pat. No. 4,103,058 byincorporating sorbent particles within the web and by employing thematerials and techniques described in more detail below to form astretchable web in which at least some of the sorbent particles areadhered to the web.

The respirators of the invention maintain a generally non-planarconfiguration and do not lie flat when in an unconstrained state. Theycan be manufactured by fabricating multiple layers of air-permeablematerials, forming the layers into the desired shape using, e.g., amolding process, optionally affixing the layers together to helpmaintain the desired shape using, e.g., an edge welding process, andattaching any other desired parts such as straps, exhalation valves andnosepieces. Features such as flexible tabs 15, noseband 16, exhalationvalve 18 and facial gasket 29 of the respirator shown in FIGS. 1 and 2can readily be omitted, but their inclusion helps the wearer achieve acomfortable, leak-free fit, and reduces condensation within therespirator or on the wearer's safety goggles or eyeglasses.

The respirator layers need not all have the same degree of airpermeability. They merely should collectively be sufficiently permeableto permit relatively easy inhalation by the respirator wearer during thedesired wearing period. Also, although the term “layer” is used todescribe materials used to form the respirator, any layer may in fact beformed from several sublayers which have been combined to obtain adesired thickness or weight. The various enumerated layers of therespirator need not be located adjacent to one another. For example, theair-permeable particle-containing layer can be separated from one orboth of the air-permeable particle-retaining layers by layers performingother functions.

The air-permeable particle-retaining layers can be the same as ordifferent from one another. They should entrap or otherwise prevent theescape of sorbent particles which may accidentally become detached fromthe air-permeable sorbent-particle-containing layer. Desirably, one ormore of the particle-retaining layers has a sufficient degree offiltration efficiency to enable it to entrap airborne particulates(e.g., particles or fibers) carried in the incoming ambient air or theoutgoing exhaled air. Preferably one or more of the particle-retaininglayers will entrap or otherwise capture particles having diameters assmall as 100 micrometers, more preferably as small as 30 micrometers,and most preferably in submicron sizes. The particle-retaining layerspreferably are arranged upstream and downstream from (i.e., with respectto the inhaled air flow) and adjacent to the particle-containing layer.A wide variety of materials can be used to form the air-permeablesorbent-particle-retaining layers. Webs made from nonwoven natural orsynthetic fibers or mixtures thereof are preferred. Suitable naturalfibers include wool, silk and cellulosic fibers such as cotton, wood orpaper pulp. Suitable synthetic fibers include polyolefins such aspolyethylene and polypropylene, polyesters, polyamides, and blends,laminates and copolymers thereof. “Copolymer” as used herein refers topolymers containing two or more monomers, including terpolymers,tetrapolymers, etc. Thermoplastic or non-thermoplastic materials can beemployed, although thermoplastic materials are generally preferred inorder to facilitate assembly of the respirator via welding. Woven ornon-woven materials can be employed, with non-woven materials beingpreferred for most applications. Melt-blown or spunbond techniques canbe employed to make such non-woven webs. Non-woven webs can also beprepared on a Rando Webber (Rando Corporation, Macedon, N.Y.) air-layingmachine or on a carding machine. Preferably the filtration efficiency ofthe particle-retaining layer is enhanced by means such as incorporationof an electret charge. If the particle-retaining layer will merelyentrap particles dislodged from the particle-containing layer, then thebasis weight and material cost for the particle-retaining layer shouldin general be kept as low as possible. If, however theparticle-retaining layer will also serve as a filtration layer, then thedesired filtration efficiency should be used as a guide to choosing thedesired web materials, basis weight and other web characteristics. Forexample, different particle-retaining filtration layers might beselected to conform to each of the nine current NIOSH certificationrequirements for non-powered air-purifying particulate respirators setout in 42 CFR Part 84, subpart K.

The air-permeable particle-containing layer should be stretchable duringshaping to a cup-like shape without tearing or significant loss ofparticles. The layer can be elastomeric (i.e., capable of recovering itsapproximate original dimensions after being stretched by a specifiedamount below the breaking point) or it can exhibit dead stretch (i.e.,capable of being stretched but then generally not returning td itsapproximate original dimensions). In general, particle-containing layersthat exhibit dead stretch are preferred. Although on a microscopic levelthere will almost always be some degree of tearing, the air-permeableparticle-containing layer should be should not exhibit visible tearingof the layer when stretched to the extent required for the actualrespirator shaping operation. The actual shaping conditions will varybut for a molding operation will usually include factors such as moldingtemperature and pressure, cycle time, and mold topography. As a generalguide for an inline molding operation intended to form a typicalcup-shaped respirator, the particle-containing layer preferably exhibitsat least about 25% elongation to break in both the machine and crossdirection, and more preferably exhibits at least about 30%, mostpreferably at least about 50%, elongation to break in at least one ofthe machine and cross directions.

When stretched, the particle-containing layer also should not exhibitsignificant loss of particles. The actual level of permissible particleloss will vary depending upon the desired respirator configuration andintended service environment. For example, as a general guide for arespirator intended to be used in the presence of typical organicvapors, the respirator preferably retains sufficient particles duringshaping so that when the respirator is evaluated using the n-hexane testmethod described below in Example 1, at least 60 minutes, and morepreferably at least 90 minutes will elapse before a level of 10 ppmhexane can be detected inside the respirator. Particle retention canalso be evaluated without the need to fabricate a finished respirator byusing the shake test described below in Example 1 to evaluate theparticle-containing web by itself Preferably, when evaluated using sucha shake test, the particle-containing layer retains at least about 90weight percent, and more preferably about 95 weight percent, and mostpreferably at least about 99 weight percent of the particles originallypresent in the layer when it was formed.

The particles preferably are adhered to the fibers in theparticle-containing layer. The actual nature of the adhesion will dependon the particles and fibers that are employed and the manner in whichthe particles are introduced into the web. Adhered particles willdesirably exhibit “area contact” with one or more adjacent fibers, thatis, they will appear to make more than mere point contact at areas wherea fiber may touch a particle. Often area contact will be indicated bythe presence of necking as is shown, for example in FIG. 3 between fiber32 and particle 33 a.

At least some of the fibers in the particle-containing layer shouldexhibit sufficient tackiness after being formed by themselves into aparticle-free web and cooled to room temperature (20° C.) so that theweb will adhere to itself. This can be evaluated manually but should becarried out promptly after the web reaches room temperature. The cooledweb can be folded over upon itself and then manually pulled apart todetermine whether or not the web layers have adhered to one another.

The particle-containing layer desirably is formed using the apparatusdiscussed, for example, in Wente, Van A., “Superfine ThermoplasticFibers”, Industrial Engineering Chemistry, Vol. 48, pages 1342-1346;Wente, Van A. et al., “Manufacture of Superfine Organic Fibers”, ReportNo. 4364 of the Navel Research Laboratories, published May 25, 1954; andin U.S. Pat. No. 3,825,379 (Lohkamp et al.) and U.S. Pat. No. 3,849,241(Butin et al.). The microfine fibers described in these references aretermed melt blown fibers and are generally substantially continuous andform into a coherent web between the exit die orifice and a collectingsurface (the “collector”) by entanglement of the microfibers due in partto the turbulent airstream in which the fibers are entrained. Whenformed by meltblown processes, the individual fibers generally have aneffective fiber diameter about 100 microns or less in diameter, morepreferably about 50 microns or less in diameter, and most preferablyabout 10 microns or less in diameter. The particle-containing layer canalso be formed by other conventional melt spinning processes, such asspunbond processes. When formed by melt spinning processes, the fibersof the particle-containing layer preferably are about 100 microns orless in diameter.

The fibers in the particle-containing layer can includepressure-sensitive adhesive fibers that will impart durable tackiness tothe particle-containing layer sufficient to enable a particle-free webformed from such fibers to adhere temporarily to itself. However, fibersthat are not durable pressure-sensitive adhesives cAn also be employed,so long as the fibers are sufficiently tacky for a temporary periodafter a particle-free web is formed from such fibers on a collector andcooled to room temperature (e.g., for at least about 30 seconds,preferably for at least about two hours, and most preferably for atleast about one or more days duration) so that the web will adhere toitself. For brevity, the pressure-sensitive adhesive fibers and thetemporarily tacky fibers will be referred to collectively as “adhesivefibers”.

The particle-containing layer preferably also includes non-adhesivefibrous material intimately commingled with the adhesive fibers toprovide the layer as a whole with suitable tensile strength,breathability, moldability and other desired properties. The commingledadhesive fibers and non-adhesive fibrous material can be present inseparate individual fibers, or as distinct regions in a conjugate fiber,or as part of a blend. For example, conjugate fibers can be in the formof two or more layered fibers, sheath-core fiber arrangements or in“island in the sea” type fiber structures. Generally with any form ofmulticomponent conjugate fibers, the adhesive fiber component willprovide at least a portion of the exposed outer surface of themulticomponent conjugate fiber. Preferably, the individual components ofthe multicomponent conjugate fibers will be present substantiallycontinuously along the fiber length in discrete zones, which zonespreferably extend along the entire length of the fibers.

Conjugate fibers can be formed, for example, as a multilayer fiber asdescribed, for example, in the above-mentioned U.S. Pat. No. 5,238,733,U.S. Pat. No. 5,601,851 (Terakawa), or International Application No. WO97/2375. Multilayered and sheath-core melt blown microfibers aredescribed, for example, in the above-mentioned U.S. Pat. No. 5,238,733,the substance of which is incorporated herein by reference in itsentirety. The '733 patent describes providing a multicomponent meltblown microfiber web by feeding two separate flow streams of polymermaterial into a separate splitter or combining manifold. The split orseparated flow streams are generally combined immediately prior to thedie or die orifice. The separate flow streams are preferably establishedinto melt streams along closely parallel flow paths and combined wherethey are substantially parallel to each other and the flow path of theresultant combined multilayered flow stream. This multilayered flowstream is then fed into the die or die orifices and through the dieorifices. Air slots are disposed on either side of a row of die orificesdirecting uniform heated air at high velocities at the extrudedmulticomponent melt streams. The hot high velocity air draws andattenuates the extruded polymeric material which solidifies aftertraveling a relatively short distance from the die. The high velocityair becomes turbulent between the die and the collector surface causingthe melt blown fibers entrained in the airstream mutually to entangleand form a coherent nonwoven web. The particulate materials described inmore detail below are fed into the turbulent airstream thereby becomingincorporated into the coherent nonwoven web. This can be done, forexample, by using a macrodropper or by other known methods. Theresulting solidified or partially-solidified particle-containing layeris then formed at the collector by known methods.

Alternatively, conjugate fibers can be formed by a spunbond process suchas described in U.S. Pat. No. 5,382,400 (Pike et al.) where separatepolymer flow streams are fed via separate conduits to a spinneret forproducing conjugate fibers of a conventional design. Generally, thesespinnerets include a housing containing a spin pack with a stack ofplates which form a pattern of openings arranged to create flow pathsfor directing the separate polymer components separately through thespinneret. The spinneret can be arranged to extrude the polymervertically or horizontally in one or more rows of fibers.

An alternative arrangement for forming melt blown conjugate fibers isdescribed for example, in the above-mentioned U.S. Pat. No. 5,601,851.The polymer flow streams are separately fed to each individual dieorifice by the use of grooves cut in a distributing and/or separatingplate. This arrangement can be used to extrude different polymers fromdifferent individual orifices to provide separate distinct fibers whichform a coherent entangled web having a substantially uniformdistribution of the different fibers. By feeding two, separate polymersto an individual die orifice a conjugate fiber can be formed. Theapparatus described is suitably used in a melt blowing type arrangementwhere the die orifices are formed in a row along the die.

The adhesive fibers contain an extrudable pressure-sensitive adhesivematerial or temporarily tacky material suitable for melt blowing (e.g.,a material having an apparent viscosity of from 150 to 800 poise undermelt-processing conditions, measured by a capillary rheometer), fiberspinning or spunbond processing. With conjugate fibers or co-formedfibers of different polymers or blends formed from a single die orspinneret, the viscosities of the separate polymer flowstreams should befairly closely matched for uniform fiber and web formation, but this isnot required. In general, matching viscosities will ensure moreuniformity in the conjugate fibers by minimizing polymer mixing, whichmixing can result in fiber breakage and formation of shot (smallparticulate polymer material), and lower web tensile properties.However, the presence of discontinuous fibers or shot is not necessarilyundesirable as long as the web has the desired overall tensile andcohesive strength.

The particular materials used to form the discrete adhesive fibers,conjugate fibers or blends (of either discrete or conjugate fibers) willdepend on the desired respirator service application and, in the case ofpolymer blends or conjugate fibers, upon the chosen non-adhesive fibrousmaterials. The adhesive fiber material is preferably any hot meltextrudable copolymer or composition having a viscosity in the melt phasesuitable for fiber forming by melt processing or in the solution phasefor solution spun fibers. Suitable classes of adhesive fiber materialsinclude stretchable block copolymers, acrylates, certain polyolefins,and a variety of other tacky or temporarily tacky adhesives. Thetemporarily tacky adhesives (for example polyalphaolefins,metallocene-catalyzed polyolefins and polyurethanes) providesurprisingly good particle retention, especially at effective fiberdiameters above about 10 micrometers, and thus are preferred. “Effectivefiber diameter”, as used herein, is evaluated using the method ofExample 1. Conventional blown microfiber materials lose the ability toretain particles as the fiber diameter increases. Because larger fibersyield webs with lower pressure drops, this use of temporarily tackyadhesive fibers permits preparation of filter webs having both goodparticle retention and low pressure drop.

Stretchable Block Copolymers

Suitable stretchable block copolymers would include those formed using atackified elastomer where a preferred elastomer is an A-B type blockcopolymer wherein the A block and B blocks are configured in linear,radial or star configurations. The A block is formed of amono-alkenylarene (preferably polystyrene) block having a molecularweight between 4000 and 50,000, and preferably between 7000 and 30,000.The A block content is preferably about 10 to 50 weight percent, andmore preferably about 10 to 30 weight percent of the block copolymer.Other suitable A blocks may be formed from alpha-methylstyrene,t-butyl-styrene and other ring-alkylated styrenes, as well as mixturesthereof. The B block is formed of an elastomeric conjugated diene,generally polyisoprene, polybutadiene or copolymers thereof having anaverage molecular weight from about 5000 to about 500,000, andpreferably from about 50,000 to about 200,000. The B block dienes canalso be hydrogenated. The B block content is preferably about 90 to 50percent, and more preferably about 90 to 70 weight percent of the blockcopolymer.

The tackifying components for the stretchable block copolymers generallyare solid tackifying resins, liquid tackifiers, plasticizers or mixturesthereof. Preferably, the tackifying resins are selected from the groupof resins at least partially compatible with the polydiene B blockportion of the elastomer. Although not preferred, generally a relativelyminor amount of the tackifying resin can include resins compatible withthe A block, which when present are generally termed end blockreinforcing resins. Generally, end block resins are formed from aromaticmonomer species. Suitable liquid tackifiers or plasticizers for use inthe adhesive polymer include napthenic oils, paraffin oils, aromaticoils, mineral oils or low molecular weight rosin esters, polyterpenesand C-5 resins. Some suitable B-block compatible solid tackifying resinsinclude C-5 resins, resin esters, polyterpenes and the like. Thetackified portion of the adhesive generally represents about 20 to 300parts per 100 parts of the elastomeric phase. Preferably, this ispredominately solid tackifier. However, from 0 to 25 weight percent, andpreferably from 0 to 10 weight percent of the adhesive composition canbe liquid tackifier or plasticizer.

Suitable stretchable block copolymers for melt blown processing arediscussed in European Patent No. 0658351 which exemplifies melt-blownfibrous synthetic rubber resin type adhesives used in a disposableabsorbent article to immobilize particulate sorbents or used as apressure-sensitive adhesive attachment (e.g., for a sanitary napkin).Suitable adhesive materials exemplified therein includestyrene-isoprene-styrene triblock block copolymers, where the copolymerhas coupling efficiencies ranging from 42 to 65 percent (e.g., 58 to 35percent polystyrene-polyisoprene diblock material would be present),tackified with C-5 hydrocarbon resins (e.g., “WINGTACK PLUS” and“WINGTACK 10” tackifiers from Goodyear) and stabilized withantioxidants. Other commercially available stretchable block copolymersinclude “KRATON” block copolymers such as “KRATON D1107”, “KRATON D1112”and “KRATON G1657” block copolymers commercially available from ShellChemical Co., “FINAPRENE” copolymers commercially available from FinaOil and Chemical, “TAIPOL” styrene-butadiene stretchable blockcopolymers commercially available from Taiwan Synthetic RubberCorporation, “SEPTON SEPS” triblock copolymer commercially availablefrom Kuraray Co., and blends (including conjugate fibers) thereof.

Acrylates

Suitable acrylates would include poly(acrylates) derived from (i) atleast one monofunctional alkyl (meth)acrylate monomer (i.e., alkylacrylate or alkyl methacrylate monomer), and (ii) at least onemonofunctional free-radically copolymerizable reinforcing monomer. Thereinforcing monomer has a homopolymer glass transition temperature(T_(g)) higher than that of the monomer (i) and will increase the glasstransition temperature and modulus of the resultant copolymer. Monomers(i) and (ii) are chosen such that a copolymer formed from them isextrudable and capable of forming fibers. Preferably, the monomers usedin preparing the adhesive fibers include a monomer (i) that, whenhomopolymerized, generally has a glass transition temperature of nogreater than about 0° C., and a monomer (ii) that, when homopolymerized,generally has a glass transition temperature of at least about 10° C.The glass transition temperatures of monomers (i) and (ii) are typicallyaccurate to within ±50° C. and are measured by differential scanningcalorimetry.

Monomer (i) contributes to the flexibility and tack of the copolymer.Preferably monomer (i) has a homopolymer T_(g) of no greater than about0° C. Preferably the alkyl group of monomer (i) has an average of about4 to about 14 carbon atoms. The alkyl group can optionally containoxygen atoms in the chain thereby forming ethers or alkoxy ethers, forexample. Examples of monomer (i) include, but are not limited to,2-methylbutyl acrylate, isooctyl acrylate, lauryl acrylate,4-methyl-2-pentyl acrylate, isoamyl acrylate, sec-butyl acrylate,n-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octylacrylate, n-decyl acrylate, isodecyl acrylate, isodecyl methacrylate,and isononyl acrylate. Other examples of monomer (i) include, but arenot limited to, poly-ethoxylated or -propoxylated methoxy (meth)acrylate(i.e., poly(ethylene/propylene oxide) mono-(meth)acrylate) macromers(also known as macromolecular monomers), polymethylvinyl ethermono(meth)acrylate macromers, and ethoxylated or propoxylatednonyl-phenol acrylate macromers. The molecular weight of such macromersis typically about 100 to about 600 grams/mole, and preferably, about300 to about 600 grams/mole. They can perform the function of acrosslinker by forming physical crosslinks that result from theformation of reinforcing domains due to phase separation. Combinationsof various monofunctional monomers categorized as monomer (i) can alsobe used in making the fibers used in the invention.

Reinforcing monomer (ii) increases the glass transition temperature andmodulus of the resultant copolymer. Preferably monomer (ii) has ahomopolymer T_(g) of at least about 10° C. More preferably, monomer (ii)is a reinforcing monofunctional (meth)acrylic monomer, including anacrylic acid, a methacrylic acid, an acrylamide, and an acrylate.Examples of monomer (ii) include, but are not limited to, acrylamides,such as acrylamide, methacrylamide, N-methyl acrylamide, N-ethylacrylamide, N-methylol acrylamide, N-hydroxyethyl acrylamide, diacetoneacrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide,N-ethyl-N-aminoethyl acrylamide, N-ethyl-N-hydroxyethyl acrylamide,N,N-dimethylol acrylamide, N,N-dihydroxyethyl acrylamide, t-butylacrylamide, dimethylaminoethyl acrylamide, N-octyl acrylamide, and1,1,3,3-tetramethylbutyl acrylamide. Other examples of monomer (ii)include acrylic acid and methacrylic acid, itaconic acid, crotonic acid,maleic acid, fumaric acid, 2,2-(diethoxy)ethyl acrylate, hydroxyethylacrylate or methacrylate, 2-hydroxypropyl acrylate or methacrylate,methyl methacrylate, isobutyl acrylate, n-butyl methacrylate, isobornylacrylate, 2-(phenoxy)ethyl acrylate or methacrylate, biphenylylacrylate, t-butylphenyl acrylate, cyclohexyl acrylate, dimethyladamantylacrylate, 2-naphthyl acrylate, phenyl acrylate, N-vinyl pyrrolidone, andN-vinyl caprolactam. Combinations of various reinforcing monofunctionalmonomers categorized as monomer (ii) can also be used to make theadhesive fibers used in the invention.

The acrylate copolymer is preferably formulated to have a resultantT_(g) of less than about 25° C. and more preferably, less than about 0°C. Such acrylate copolymers preferably include about 60 parts to about98 parts per hundred of at least one alkyl (meth)acrylate monomer (i)and about 2 parts to about 30 parts per hundred of at least onecopolymerizable reinforcing monomer (ii). Preferably, the acrylatecopolymers have about 85 parts to about 98 parts per hundred of at leastone alkyl (meth)acrylate monomer (i) and about 2 parts to about 15 partsof at least one copolymerizable reinforcing monomer (ii).

A crosslinking agent can be used if so desired to build the molecularweight and strength of the copolymer, and hence improve the integrityand shape of the adhesive fibers. Preferably the crosslinking agent isone that is copolymerized with monomers (i) and (ii). The crosslinkingagent may produce chemical crosslinks (e.g., covalent bonds).Alternatively, it may produce physical crosslinks that result, forexample, from the formation or reinforcing domains due to phaseseparation or acid base interactions. Suitable crosslinking agents aredisclosed in U.S. Pat. No. 4,379,201 (Heilman), U.S. Pat. No. 4,737,559(Kellen), U.S. Pat. No. 5,506,279 (Babu et al.) and U.S. Pat. No.4,554,324 (Husman).

The crosslinking agent is preferably not activated towards crosslinkinguntil after the copolymer is extruded and the fibers are formed. Thus,the crosslinking agent can be a photocrosslinking agent, which, uponexposure to ultraviolet radiation (e.g., radiation having a wavelengthof about 250 nanometers to about 400 nanometers), causes the copolymerto crosslink. Preferably, however, the crosslinking agent providescrosslinking, typically, physical crosslinking, without furtherprocessing. Physical crosslinking can occur through phase separation ofdomains which produces thermally reversible crosslinks. Thus, acrylatecopolymers prepared from a crosslinker that provides reversible physicalcrosslinking are particularly advantageous in the preparation of fibersusing a melt process.

Preferably, the copolymerizable crosslinking agent is (1) an acryliccrosslinking monomer, or (2) a polymeric crosslinking material having acopolymerizable vinyl group. More preferably, the crosslinking agent isa polymeric crosslinking material having a copolymerizable vinyl group.Preferably, each of these monomers is a free-radically polymerizablecrosslinking agent capable of copolymerizing with monomers (i) and (ii).Combinations of various crosslinking agents can be used to make theacrylate copolymer. It should be understood, however, that suchcrosslinking agents are optional.

The acrylic crosslinking monomer is preferably one that is polymerizedwith monomers (i) and (ii) and generates free radicals in the polymerbackbone upon irradiation of the polymer. An example of such a monomeris an acrylated benzophenone such as described in the above-mentionedU.S. Pat. No. 4,737,559.

Crosslinking polymeric materials (2) that have a copolymerizable vinylgroup can preferably be represented by the general formula X—(Y)_(n)—Zwherein X is a copolymerizable vinyl group; Y is a divalent linkinggroup where n can be zero or one; and Z is a monovalent polymeric moietyhaving a T_(g) greater than about 20° C. and a weight average molecularweight in the range of about 2,000 to about 30,000 and being essentiallyunreactive under copolymerization conditions. Particularly preferredvinyl-terminated polymeric monomers (2) useful in making the acrylatecopolymers used in the invention may be further defined as having an Xgroup of the formula HR¹C═CR²— wherein R¹ is a hydrogen atom or a —COOHgroup and R² is a hydrogen atom or a methyl group; or a Z group of theformula —{C(R³)(R⁴)CH₂}_(n)—R⁵ wherein R³ is a hydrogen atom or a loweralkyl group, R⁴ is a lower alkyl group, n is an integer from 20 to 500,and R⁵ is a monovalent radical selected from the group consisting of—C₆H₄R⁶ and —CO₂R⁷ wherein R⁶ is a hydrogen atom or a lower alkyl groupand R⁷ is a lower alkyl group.

Such vinyl-terminated polymeric crosslinking monomers are sometimesreferred to as macromolecular monomers (i.e., “macromers”). Oncepolymerized with the (meth)acrylate monomer and the reinforcing monomer,a vinyl-terminated polymeric monomer of this type forms a copolymerhaving pendant polymeric moieties which tend to reinforce the otherwisesoft acrylate backbone, providing a substantial increase in the shearstrength of the resultant copolymer adhesive. Specific examples of suchcrosslinking polymeric materials are disclosed in U.S. Pat. No.4,554,324 (Husman et al.).

If used, the copolymerizable crosslinking agent is used in a curativelyeffective amount, by which is meant an amount that is sufficient tocause crosslinking of the acrylate to provide the desired final adhesionproperties in the particle-containing layer. Preferably, if used, thecrosslinking agent is used in an amount of about 0.1 part to about 10parts, based on the total amount of monomers.

If a photocrosslinking agent has been used, the adhesive in the form offibers can be exposed to ultraviolet radiation having a wavelength ofabout 250 nm to about 400 nm. The radiant energy in this preferred rangeof wavelength required to crosslink the adhesive is about 100milliJoules/square centimeter (mJ/cm²) to about 1,500 mJ/cm², and morepreferably, about 200 mJ/cm² to about 800 mJ/cm².

The acrylate copolymers used in the invention can be synthesized by avariety of free-radical polymerization processes, including solution,radiation, bulk, dispersion, emulsion, and suspension polymerizationprocesses. Bulk polymerization methods, such as the continuous freeradical polymerization method described in U.S. Pat. Nos. 4,619,979 or4,843,134 (both to Kotnour et al.), the essentially adiabaticpolymerization methods using a batch reactor described in U.S. Pat. No.5,637,646 (Ellis), and the methods described for polymerizing packagedpre-adhesive compositions described in International Patent ApplicationNo. WO 96/07522 may also be utilized to prepare the acrylate polymerfrom which the adhesive fibers can be prepared. The acrylate copolymerscan also include conventional additives such as tackifiers (wood rosin,polyesters, etc.), plasticizers, flow modifiers, neutralizing agents,stabilizers, antioxidants, fillers, colorants, and the like, as long asthey do not interfere in the fiber-forming melt process. Initiators thatare not copolymerizable with the monomers used to prepare the acrylatecopolymer can also be used to enhance the rate of polymerization and/orcrosslinking. These additives are incorporated in amounts that do notmaterially adversely affect the desired properties of the acrylatecopolymers or their fiber-forming properties. Typically, they can bemixed into these systems in amounts of about 0.05 volume percent toabout 25 volume percent of the adhesive composition.

Polyolefins

Suitable polyolefins would include tackified higher polyolefin elastomeradhesives (e.g., polybutylene adhesives), atactic or substantiallyatactic polypropylene, and amorphous polyalphaolefin polymers suitablefor forming hot melt pressure-sensitive adhesives with or without addedtackifier. Polyalphaolefins are preferred. Suitable polyalphaolefins aregenerally copolymers of a C₃ to C₅ linear alpha-olefin(s) and a higher(generally C₆ to C₁₀) alpha-olefin(s). Preferred are copolymers ofpolyolefins with polyhexene, polyheptene, polyoctene, polynonene and/orpolydecene. Preferred polyalphaolefins are described in U.S. Pat. Nos.3,954,697 and 4,072,812 (both to McConnell et al.) and U.S. Pat. No.4,684,576 (Tabor) where the amorphous polyalphaolefin copolymers can beused without added tackifiers directly to form a pressure-sensitiveadhesive. These amorphous copolymers generally have from 40 to 60 molepercent of the higher alpha olefin comonomer(s). However, suitablecompatible tackifying resins and plasticizing oils can be used whichgenerally correspond to those used to tackify the synthetic AB blockcopolymer elastomers described above. For example, suitable compatibleliquid or solid tackifiers would include hydrocarbon resins, such aspolyterpenes, C-5 hydrocarbbn resins, or polyisoprenes. Resin esters ofaromatic or aliphatic acids would be suitable. If these tackifiers areused in sufficient amounts, the higher alpha olefin content can be aslow as 15 mole percent and still provide suitable adhesive fibers.

Representative commercially-available polyolefins include “ASPUN 6805”and “ASPUN 6806” ethylene/octene copolymer, both available from DowChemical Co., “ENGAGE 8400” ethylene/octene copolymer available fromDuPont Dow Elastomers, EXACT 4023” metallocene-catalyzedethylene/butylene copolymer available from Exxon Chemical Co., “REXENED100” “EASTOFLEX D127” and “EASTOFLEX E1200” polyalphaolefins, bothavailable from Eastman Chemical Co., “VESTOPLAST V520” and “VESTOPLASTV750” polyalphaolefin, both available from Hüls America Inc., and blends(including conjugate fibers) thereof.

Other Tacky or Temporarily Tacky Adhesives

Other tacky or temporarily tacky adhesive materials for use in formingthe particle-containing layer include polyurethanes such as “MORTHANE440” and “MORTHANE 455” polyester-based polyurethanes, both availablefrom Morton International, “PELLETHANE” polyester-based polyurethanessuch as “PELLETHANE 2355-85ABR” polyurethane available from Dow ChemicalCo., “ESTANE” polyurethanes such as “ESTANE 58238” and “ESTANE 58661”polyester-based polyurethanes, both available from B.F. GoodrichSpecialty Plastics., polydiorganosiloxane polyurea copolymers of thetype disclosed in copending U.S. patent application Ser. No. 08/980,925filed Dec. 1, 1997, the disclosure of which is expressly incorporatedherein by reference, and blends (including conjugate fibers) thereof.

Non-Adhesive Fibrous Material

As mentioned above, the particle-containing layer can includenon-adhesive fibrous material, as separate individual fibers, or asdistinct regions in a conjugate fiber, or as part of a blend. Suitablenon-adhesive fibrous materials include lower polyolefins such aspolyethylene and isotactic polypropylene, polyesters, polyamides,polystyrenes, and non-tacky polyurethanes.

The non-adhesive fibrous material generally represents from 0 up toabout 90 percent of the basis weight of the fibers in theparticle-containing layer, more preferably about 60 to about 80 percent.When the non-adhesive fibrous material is present as a discrete fiber,the fibers are generally intimately commingled with the adhesive fibers.Such commingled fibers can be formed from the die described in theabove-mentioned U.S. Pat. No. 5,601,851 or in a separate die which coulddirect the non-adhesive fibrous material directly, or subsequently, intothe fiber stream containing the adhesive fibers prior to formation ofthe commingled fiber web on the collector. The use of multiple dies forforming other types of commingled fibers is known in the art.

Generally, depending on the fiber formation process, suitableantioxidants and heat stabilizers could be used in the present inventionto prevent the degradation of the particle-containing layer during thefiber forming process or in use. Also, other conventional additivescould be used such as UV absorbents, pigments, particulates, staplefibers or the like.

A variety of particles can be employed in the particle-containing layer.Desirably the particles will be capable of absorbing or adsorbing gases,aerosols or liquids expected to be present under the intended serviceconditions. The particles can be in any useful form including beads,flakes, granules or agglomerates. Useful particles include activatedcarbon, alumina and other metal oxides, clay, hopcalite and othercatalysts, ion exchange resins, molecular sieves and other zeolites,silica, sodium bicarbonate, biocides, fungicides and virucides.Activated carbon and alumina are preferred particles. Mixtures ofparticles can be employed, e.g., to absorb mixtures of gases, althoughin practice it generally is better to employ separateparticle-containing layers to deal with mixtures of gases. The desiredparticle size will depend on the intended service conditions. As ageneral guide, particle sizes between about 30 and about 800 micrometersare preferred, and particle sizes between about 100 and about 300micrometers are most preferred.

Preferably, the particles are present in amounts sufficient to providethe desired degree of filtration and absorption in the finishedrespirator. The precise amount will depend on factors such as theparticle type and surface area and the desired pressure drop, servicelife and other relevant respirator properties. As a general guide, goodresults can be obtained using particle-containing layers having about 65to 97%, more preferably about 70 to about 80% particles, compared to thetotal weight of the particle-containing layer. For webs containingcarbon particles, the carbon weight is preferably about 50 to about 750g/m², and more preferably about 50 to about 250 g/m².

Pillowed particle-containing webs can be used by adapting themanufacturing procedures described in the above-mentioned U.S. Pat. No.4,103,058 (Humlicek), employing fibers that are sufficiently stretchableand by fabricating the web under conditions that will adhere theparticles to the web. Pillowed webs exhibit particularly useful moldingproperties and are preferred for use in the respirators of theinvention.

At least one of the respirator layers is a shape-retaining layer or“shaping layer”. Shaping layers can serve as one or both of theparticle-retaining layers. Often however a lower weight or lower costrespirator can be formed by using a separate shaping layer or layerswhose shaping function is not compromised by the need to retainparticles. However, the shaping layer can perform functions other thanshaping, such as protection of the other layers of the respirator orprefiltration of a particulate stream. In some embodiments only oneshaping layer need be included in the respirator, but shaping can beaccomplished more durably and conveniently if two shaping layers areused, for example, inner and outer shaping layers as shown in FIGS. 2and 5.

The shaping layer preferably contains fibers having bonding componentswhich, after the particle-containing layer formed into a cup-like shape,will allow the fibers to be bonded to one another at points of fiberintersection. This can be accomplished, for example, by using fiberscontaining bonding components which allow adjacent contacting fibers tocoalesce when subjected to heat and cooled. Such thermally bondingfibers typically come in monofilament and bicomponent form. Bicomponentfibers are the preferred fibers for use in forming shaping layers ofthis invention. Suitable bicomponent fibers include, for example,coextensive side-by-side configurations, coextensive concentricsheath-core configurations such as MELTY fibers from Unitika Limited,SOFFIT fibers from Kuraray (marketed in the US by Chori America, Inc.),and coextensive elliptical sheath-core configurations such as CHISSO ESfrom Chisso, Inc. (marketed in the US by Marubeni Corp.) Oneparticularly useful bicomponent fiber for producing shaping layers has agenerally concentric sheath-core configuration having a core ofcrystalline polyethylene terephthalate (PET) surrounded by a sheath ofan amorphous copolyester. This bicomponent fiber is manufactured byUnitika Limited and is sold as MELTY Type 4080 fiber. Anotherparticularly suitable bicomponent fiber is a concentric sheath/corefiber having a core of crystalline PET and a sheath of a modifiedcopolyolefin (such as the copolymer described in the above-mentionedU.S. Pat. No. 4,684,576), for example, CELBOND Type 254 and 255 fibersmade by Hoechst Celanese. The fibers in the shaping layer are usuallybetween 1 and 200 denier and preferably average greater than 1 denierbut less than 50 denier. In preferred embodiments, the shaping layer orlayers contain a mixture of synthetic staple fiber (preferably crimped)and bicomponent binder fiber. Shaping layers which maintain low degreesof surface fuzz and provide a high degree of wearer comfort can beprepared as described in the above-mentioned U.S. Pat. No. 5,307,796.

Binder fibers are typically made from polymeric materials that softenand bond to other fibers when heated and cooled. Binder fibers willtypically retain their fibrous structure after bonding. Examples ofbinder fibers are KODEL Type 444 fibers made by Eastman Chemical, andType 259 fibers made by Hoechst Celanese. Upon heating of the non-wovenweb, the binder fibers soften and adhere to adjacent-contacting fibers.When the non-woven web is cooled in the molding step, bonds develop atfiber intersection points.

Bonding components such as acrylic latex may be applied to a web offibers in order to form a shaping layer. Also, bonding components in theform of powdered heat-activatable adhesive resins may be cascaded onto aweb of fibers, whereupon when the web is heated the fibers in the webbecome bonded together at intersection points by the added resin.Shaping layers of the invention preferably are free from such addedbonding components because they increase material and processing costsand can contribute to increased flammability of the finishedrespirators.

Staple fibers suitable for use in forming respirator shaping layers arenon-thermally bonding fibers, typically, synthetic single componentfibers such as fibers made from polyethylene terephthalate (PET), nylon,and rayon. PET fibers (such as TREVIRA Type 121 and 295 fibers made byHoechst Celanese) are preferred staple fibers.

The outer and inner shaping layers preferably contain a mixture ofbicomponent fibers and staple fibers. For example, the outer shapinglayer preferably contains about 70 weight-percent bicomponent fibers andabout 30 weight-percent staple fibers, and the inner shaping layerpreferably contains about 60 weight percent bicomponent fibers and 40weight percent staple fibers. The outer shaping layer preferablyprovides a greater degree of support for the respirator than the innershaping layer by having a greater basis weight or by containing agreater proportion of bicomponent fiber.

If only a low degree of filtration is needed, the respirators of theinvention can employ the layers mentioned above without furtherfiltration layers. The particle-retaining layers and theparticle-containing layer typically will be capable of some degree ofincoming and outgoing air filtration, and can screen out largerparticles such as saliva from the wearer and relatively largeparticulate matter in the air. However, the respirators of the inventionpreferably also contain a filtration layer which entraps or otherwiseprevents the ingress of undesired small particles such as sawdust,insulation materials, soot particles and the like. The fibers selectedfor use in a filtration layer will depend upon the kind of particulateto be filtered. Particularly useful filtration layers can be made fromwebs of melt-blown fibers, such as those disclosed in Wente, Van A.,“Superfine Thermoplastic Fibers”, id at 1342 et seq. Webs of meltblownfibers provide especially good filtration layers when used in apersistent electrically charged form as described, for example, in U.S.Pat. No. 4,215,682 (Kubik et al). Preferably, these melt-blown fibershave an average diameter of less than about 10 micrometers. Otherparticularly useful filtration fibers areelectrically-charged-fibrillated-film-fibers as disclosed in U.S. Pat.No. RE 31,285 (Van Turnhout), and commercially-available filtrationmaterials such as TECHNOSTAT Type E200 web from All Felt Products, Inc.Rosinwool fibrous webs and webs of glass fibers are also usefulfiltration layers, as are solution blown, or electrostatically sprayedfibers, especially in microfiber form.

Preferred respirators of this invention contain at least one filtrationlayer containing blown micro-fibers, preferably electrically-chargedblown micro-fibers. The filtration layer preferably is disposed betweentwo shaping layers and preferably is upstream, or both upstream anddownstream, from the particle-containing layer. Most preferably therespirator contains two filtration layers, each of which is anelectrically-charged web, located upstream and downstream from theparticle-containing layer. The web from which one or more of thefiltration layers are formed can optionally be heat set (e.g., attemperatures of 260° C. to 425° C.) using infrared heaters located aboveand below the web before it is combined with the other layers used toform the respirator.

The respirator layers can be formed into the desired final respiratorconfiguration using conventional respirator manufacturing techniques.For example, the layers can be stacked together and molded at room orelevated temperatures between mating male and female molds. The variouslayers can be molded together all at once or in separate subassemblieswhich are later joined together. The mating mold halves need not match,and uniform or non-uniform mold gaps can be employed across the surfaceof the respirator. Mold gaps of, e.g., about 1 mm to about 8 mm can beemployed, and may allow the various layers (e.g., the filter layer) tomove within the mold without tearing the adjacent layers.

A variety of conventional assembly techniques can be used to jointogether the various layers to form the completed respirator. Usefultechniques include ultrasonic welding, adhesive bonding, thermalbonding, needle tacking and stitched seams.

The invention will be further illustrated by the following examples, inwhich all parts and percentages are by weight unless otherwiseindicated.

EXAMPLE 1 AND CONTROL EXAMPLE 1

A particle-loaded web was prepared as follows. The web was made frommulti-layer melt-blown microfibers prepared as described in theabove-mentioned U.S. Pat. No. 5,238,733. Two polymeric materials wereseparately introduced by separate extruders into a coextrusionfeedblock. The first material was EASTOFLEX D127S amorphous polyolefin,obtained from Eastman Chemical Co. This material has pressure-sensitiveadhesive properties and will be referred to as the PSA component. Thesecond material was ESCORENE 3505 G isotactic polypropylene, obtainedfrom Exxon Chemical Co., and will be referred to as the polypropylenecomponent. The coextrusion feedblock split the PSA component into twoflowstreams and combined them with the polypropylene componentflowstream, forming a single layered flowstream having a layer ofpolypropylene sandwiched between top and bottom layers of the PSA. Thislayered flowstream was fed immediately into a melt-blowing die havingcircular smooth surface orifices with a 6.86:1 length to diameter ratio.The primary air was maintained at 285° C. and 151 KPa with a 0.076 cmgap width to produce a uniform web. The die was maintained at 285° C.,and the die was operated at a rate of 187 g/hr/cm die width. The web wascollected on a rotating drum collector at a collector to die distance of30.4 cm.

Activated carbon particles were incorporated into the web by droppingthem into the freshly blown stream of meltblown fibers after the fibersexited from the die and before they reached the collector, using thegeneral procedure described in U.S. Pat. No. 4,429,001 (Kolpin et al.).The particles were Calgon Activated Carbon, 40×140 mesh (105 micrometersto 379 micrometers), obtained from Calgon Carbon Corp., Pittsburgh, Pa.The resulting particle-loaded web contained bicomponent fibers having agenerally layered PSA/polypropylene/PSA structure, and a composition of76% polypropylene and 24% PSA. The web had a basis weight of 375 gramsper square meter and contained 80% carbon particles and 20% bicomponentfibers.

Web samples were evaluated for effective fiber diameter according to themethod set forth in Davies, C. N., “The Separation of Airborne Dust andParticles,” Institution of Mechanical Engineers, London, Proceedings 1B,1952.

Web samples 2.54 cm in width were evaluated for tensile strength and %elongation to break in both the machine and cross-web directions using aTexture Analyzer Model TA-XT2 operated at a 10 mm/sec crosshead speedusing an 80 mm gauge length.

Web samples were also evaluated for particle retention using a shaketest performed as follows. The sample web was placed atop a sheet ofpaper and three 171.5 mm circular samples of both the web and paper werecut using a circular die. The paper collected any particles (e.g.,carbon) that fell from the samples during the subsequent weighing step.Taking care to minimize the overall amount of sample handling, thesamples and any particles that had collected on the paper were weighedtogether. The samples were placed in three standard sieves (of any sizebetween US Standard No. 8 and No. 14). Each sample was affixed in asieve using four twisted paper clips that were spaced equally around thecircumference of the sample, threaded through the sieve screen, andfolded over to pierce and anchor the sample to the screen. Twenty USpennies were placed atop each sample to act as impact media. Each sievewas then stacked atop a fresh sieve whose interior had been lined withpaper to serve as a carbon collection surface. The three sets of sampleand collector sieves were stacked one atop another to form a stackcontaining six sieves. The stack was capped with a lid and a base andagitated in a Model B RoTap Testing Sieve Shaker (Tyler IndustrialProducts) for ten minutes. The samples were removed and reweighed, andthe weight percent of retained particles calculated. Because samples atthe top of the sieve stack had a tendency to lose more particles thansamples at the bottom of the stack, the average of the three samples wasused to determine particle loss.

Shaping layers were made on a Double Rando Webber air-laying machine bycombining 65% Type 254 bicomponent fibers, 15 denier (Hoechst-CelaneseCorp.) with 35% Type 295 staple fibers, 15 denier (Hoechst-CelaneseCorp.) Each shaping layer had a basis weight of 63 grams per squaremeter.

A filter layer having an electret charge was prepared from a blownmicrofiber web made from ESCORENE 3505 G polypropylene (Exxon ChemicalCo.) and having a basis weight of 56 grams per square meter. The web wascharged by subjecting it to a corona discharge treatment followed byimpingement of jets of water as described in U.S. Pat. No. 5,496,507(Angadjivand et al.).

A molded respirator was then prepared by stacking one of the shapinglayers, the particle-loaded web, the filter layer having an electretcharge, layer having an electret charge, and the other shaping layer.This was accomplished while forming the shaping layers on the DoubleRando Webber machine, by feeding the particle-loaded web and theelectret filter web between the two shaping layers.

A respirator was molded from the stacked assembly of webs using thegeneral procedure described in the above-mentioned U.S. Pat. No.4,536,440. The molds were heated to a temperature of 114-118° C., andthe web assembly was compressed to a mold gap of 0.13 cm. The dwell timewas 12-15 seconds. The molded respirators were inspected for signs ofweb separation or tearing, and none was observed. Two further layerswere added to the respirator. The outermost layer was a flame-retardantshaping layer made by combining 40% Type 295 polyester staple fibers, 15denier (Hoechst-Celanese Corp.), 40% polyester staple fibers, 50 denier,and 20% Type 259 binder fibers, 3 denier (Hoechst-Celanese Corp.) andcoating the resulting web with “FYARESTOR 330B” flame retardant(PYRO-CHEK Division of Ferro Corporation) at an add-on weight of 37.5%of the total web weight. The finished web had a basis weight of 180grams per square meter. Under the outermost layer was placed aprefiltration layer made by combining 50% Type 180 polyester staplefibers, 1.35 denier (Hoechst-Celanese Corp.) with 50% 7 micrometeraverage diameter blown microfibers. The resulting web had a basis weightof 200 grams per square meter. The two layers were ultrasonically weldedto the respirator and excess material trimmed away.

Samples of the molded respirators were evaluated against an ozonechallenge as follows. The respirator sample was mounted on a breathingmachine operating at 24 strokes per minute and a 40 liter per minuteflow rate through the respirator. The respirator was exposed to anatmosphere containing 5 ppm ozone (generated using an Orec Model 03V1-0Ozone Generator) at 50% Relative Humidity (±3%) and 35° C. (±2° C.).Ozone penetrating through the respirator was detected with a DasibiModel 1003-AH Ozone Monitor. The ozone level in parts per million (ppm)was measured 48 minutes after the start of the evaluation.

Samples of the molded respirators of the invention were evaluatedagainst an organic vapor (OV) challenge, using n-hexane as the organicvapor. A respirator sample was mounted on the above-described breathingmachine and exposed to an atmosphere containing 60 ppm n-hexane at 50%Relative Humidity (±3%) and 35° C. (±2° C.). The flow rate through therespirator was 20 liters per minute. Hexane penetration through therespirator was detected with an HNU Model PI-201 PhotoionizationMonitor. The time in minutes required to detect 10 ppm hexane inside therespirator chamber was recorded.

Comparison respirators (identified in the table below as “Control 1”)were formed largely from the same layers and similarly evaluated.However, in place of the particle-containing layer the respirators werefabricated using a preform prepared according to the general procedureof Example 22 of the above mentioned U.S. Pat. No. 4,807,619 andcontaining 128 grams per square meter of carbon particles.

The resulting evaluation data is set out below in Table 1:

TABLE 1 Respirator Example 1 Control 1 Basis Weight, g/m², particle- 375160 containing layer Wt. % particles in particle- 80 80 containing layerEffective fiber diameter, μm 10.9 8.0 MD Elongation, % 11.9 3.2 CDElongation, % 58.3 4.2 MD Tensile, g 1017 513 CD Tensile, g 1060 331 %Particles retained in shake 99.2 83.8 test Ozone level, ppm 0.064 after48 0.100 after 5 minutes minutes Hexane level, time to detect 10 138 29ppm, minutes

EXAMPLE 2

In this example, a particle-loaded web was prepared as in Example 1using alumina particles instead of activated carbon. The aluminaparticles were obtained from Rhone-Poulenc, Inc., Monmouth Junction,N.J. and had a particle size distribution of 36 to 297 micrometers. Theparticle-loaded web had a basis weight of 220 grams per square meter andthe alumina particles were 65% of the total web weight.

The particle-containing web was assembled with a flame-retardant shapinglayer, a prefiltration layer, shaping layers and filtration webs asdescribed in Example 1. The molded respirators were inspected for signsof web separation or tearing, and none was observed.

Samples of the molded respirators were evaluated with a hydrogenfluoride challenge as follows. The respirator was mounted on a breathingmachine as in Example 1 with a flow rate through the respirator of 64liters per minute and challenged with an atmosphere containing 70 ppmhydrogen fluoride and 50% Relative Humidity (±3%) and 23° C. (±2° C.).Hydrogen fluoride in the respirator cavity was measured with a SensidyneHF Detector. The time required to detect 3 ppm hydrogen fluoride in therespirator cavity was recorded. Times greater than 30 minutes areconsidered passing under 42 CFR §84.190. The average measured time forthe molded respirator samples was 183 minutes.

In an effort to determine whether molding the respirators had stretchedthe particle-containing web close to its breaking point, strips of themolded respirator were cut out, and the particle-containing layer wasremoved and evaluated for percent elongation before break as inExample 1. The elongation to break in the machine direction was 11.8%and in the cross direction it was 45.5%.

EXAMPLE 3

A particle-loaded web was prepared as in Example 2 except the basisweight was increased to 309 grams per square meter by lowering thecollector speed. The percent load was 62% alumina particles. Theparticle-containing web was assembled with a flame-retardant shapinglayer, a prefiltration layer, shaping layers and filtration webs asdescribed in Example 1. No sign of web separation or tearing wasobserved.

The respirators were evaluated as in Example 2. The time required todetect 3 ppm hydrogen fluoride in the respirator cavity in the hydrogenfluoride challenge test was 235 minutes, compared with a minimumsatisfactory time of 30 minutes. The percent elongation of theparticle-containing layer after molding was 10.2% in the machinedirection and 42.8% in the cross direction.

EXAMPLE 4

A particle-loaded web was prepared as described in Example 1 except thebasis weight of the web was increased by lowering the collector speed.The basis weight of the web was 473 grams per square meter and theactivated carbon was 68% of the weight of the web. The effective fiberdiameter was 10.9 micrometers. Using the shake test of Example 1, 99.4%of the carbon particles were retained on the web. Theparticle-containing web was assembled with a flame-retardant shapinglayer, a prefiltration layer, shaping layers and filtration webs asdescribed in Example 1. No sign of web separation or tearing wasobserved.

Samples of the molded respirators were evaluated as described in Example1 for ozone resistance, organic vapor resistance, and pressure drop. Theozone level was 0.02 ppm after 48 minutes and the time to detect 10 ppmhexane was 168 minutes. The pressure drop at a flow rate of 85 litersper minute was 10.2 mm H₂O.

EXAMPLES 5-6

Particle-loaded webs were prepared as described in Example 1 except thatthe activated carbon had a smaller average particle size, namely 80×325mesh (46 to 187 micrometers). The basis weights, percent particles andshake test results for the particle-containing webs are given in Table2. The particle-containing web was assembled with a flame-retardantshaping layer, a prefiltration layer, shaping layers and filtration websas described in Example 1. No sign of web separation or tearing wasobserved.

The molded respirators were evaluated for ozone resistance, organicvapor resistance, and pressure drop. Strips were cut from therespirators in both the machine direction and cross-direction in whichthe particle-containing layer had been made. The elongation to break andthe tensile strength of the particle-containing layer after molding weremeasured and are shown in Table 2.

TABLE 2 Example 5 6 Basis Weight, g/m², particle- 388 500 containinglayer % Particles 73.4 73.3 % Particles retained in shake test 99.3 99.1Ozone level, ppm after 48 0.012 0.009 minutes Hexane level, time todetect 10 174 183 ppm, minutes Pressure drop, mm H₂O 12.6 19.8 MDElongation, % 10.6 12.0 CD Elongation, % 23.4 22.1 MD Tensile, g 11291991 CD Tensile, g 1050 1668

EXAMPLE 7

A particle-loaded web was prepared as described in Example 1 except theweb was collected on a perforated collector having circular openings,producing a web with a pillowed configuration like that shown in FIG. 6.The diameter of the perforations was 0.79 cm. and the land area was44.75%. The collector was approximately 18 cm. from the die. The basisweight of the web was 392 g/²and the activated carbon was 70% of theweight of the web. When evaluated using the shake test of Example 1, 97%of the particles were retained in the web. The particle-containing webwas assembled with a flame-retardant shaping layer, a prefiltrationlayer, shaping layers and filtration webs as described in Example 1. Nosign of web separation or tearing was observed.

Samples of the molded respirators were evaluated as described in Example1 for ozone resistance, organic vapor resistance, and pressure drop. Theozone level was 0.007 ppm after 48 minutes and the time to detect 10 ppmhexane was 161 minutes. The pressure drop at a flow rate of 85 litersper minute was 8.5 mm H₂O.

Strips were cut from the respirators in both the machine direction andcross direction in which the particle-containing layer had been made.The particle-containing layer had become flattened during the moldingprocess and had lost much but not all of its pillowed appearance. Theelongation to break of the particle-containing layer was in the machinedirection was 9% and in the cross direction it was 36.5%. The tensilestrength was 1482 grams in the machine direction and 796 grams in thecross direction.

EXAMPLES 8-10

Particle-loaded webs were prepared as described in Example 1 except thepolymeric material was a single component and the polymer was fed fromthe extruder directly into the die. In Example 8 the polymer was EXACT4023 metallocene-catalyzed ethylene/butylene copolymer from ExxonChemical Co. In Example 9 the polymer was MORTHANE 440-200 polyurethanefrom Morton International and in Example 10 the polymer was MORTHANE455-200 polyurethane from Morton International. The basis weights andparticle percentages of the webs are shown in Table 3. Strips were cutfrom the unmolded webs in both the machine direction and crossdirection. The elongation to break and the tensile strength of the webswere measured and are shown in Table 3.

TABLE 3 Example 8 9 10 Polymer EXACT 4023 MORTHANE MORTHANEethylene/butylene 440 455 copolymer polyurethane polyurethane BasisWeight, g/m², 128 136 92 particle-containing layer % Particles 52 64 46MD Elongation, % 79.4 79.7 79.3 CD Elongation, % 79.5 79.8 79.8 MDTensile, g 138 212 181 CD Tensile, g 117 156 133

EXAMPLE 11

A particle-loaded web was prepared as described in Example 1 except theamorphous polyolefin was EASTOFLEX 1200 from Eastman Chemical Co. Theweb had a basis weight of 300 grams per square meter and contained 80%carbon particles and 20% bicomponent fibers. The particle-containing webwas assembled with a flame-retardant shaping layer, a prefiltrationlayer, shaping layers and filtration webs as described in Example 1. Nosign of web separation or tearing was observed.

Samples of the molded respirators were evaluated as described in Example1 for ozone resistance and organic vapor resistance. The ozone level was0.04 ppm after 48 minutes and the time to detect 10 ppm hexane was 89minutes.

EXAMPLE 12

A particle-loaded web was prepared from commingled fibers using twoseparate extruders and dies arranged to blend their outputs and form asingle web. The first extruder contained EASTOFLEX E1200 amorphouspolyolefin and the second extruder contained ESCORENE 3505 Gpolypropylene. The molten extrudates were fed to conventional NavalResearch Lab melt-blowing dies having circular smooth surface orificeswith a 20:1 length to diameter ratio. The primary air was maintained at252° C. and 24.8 KPa with a 0.0381 cm gap width. Both dies weremaintained at 316° C. The amorphous polyolefin die was operated at arate of 107 g/hr/cm die width, and the polypropylene die was operated ata rate of 428 g/hr/cm die width. Calgon Activated Carbon particles(40×140 mesh) were dropped into blown streams of microfibers after theyexited the dies and before the fibers reached the rotating drumcollector. The collector to die distance was 30.4 cm. The resultingparticle-containing layer had a basis weight of 300 grams per squaremeter and an effective fiber diameter of about 10 micrometers, andcontained about 76% carbon particles and 24% commingled fibers, with 18%of the commingled fibers being polyalphaolefin and 82% beingpolypropylene. The particle-containing web was assembled with aflame-retardant shaping layer, a prefiltration layer, shaping layers andfiltration webs as described in Example 1. No sign of web separation ortearing was observed. Samples of the molded respirators were evaluatedas described in Example 1 for ozone resistance and for organic vaporresistance. After 48 minutes the ozone level reached 0.045 ppm, and thetime to detect 10 ppm hexane was 79 minutes.

EXAMPLES 13-23 AND CONTROL EXAMPLES 2-13

Using the method of Example 1, two series of particle-containing webshaving varying effective fiber diameters were prepared and evaluated forparticle retention. The first series (identified in Table 4 below asExamples 13-23) employed adhesive fiber materials, and the second series(identified in Table 4 below as Control 2-13) employed non-adhesivefiber materials. Each of the webs contained carbon particles, in variousmesh sizes. Set out in Table 4 below is the Example number or ControlExample number, the fiber material (identified in greater detail in thekey below the table), the carbon mesh size, initial weight percentcarbon, percent carbon retained in the shake test, and the effectivefiber diameter for each web.

TABLE 4 Initial % Carbon Effective Fiber Carbon % retained in fiberMaterial Mesh Size Carbon shake test diameter, μm Example 13 E4023 40 ×140 80.0 99.8 19.5 Example 14 E1200 40 × 140 81.5 95.4 19.8 Example 15E1200 80 × 325 80.0 99.7 19.8 Example 16 PUR440 40 × 140 77.3 98.5 22.3Example 17 PUR440 80 × 325 70.6 92.4 22.3 Example 18 PUR440 12 × 20 80.993.9 24.5 Example 19 E1200 40 × 140 81.0 99.7 27 Example 20 E1200 80 ×325 77.0 99.8 27 Example 21 PUR455 40 × 140 76.2 99.3 35 Example 22PUR455 80 × 325 66.7 98.3 35 Example 23 PUR455 12 × 20 80.2 97.7 37.5Control 2 F3860 40 × 140 77.8 83.8 6.4 Control 3 E3795 80 × 325 81.591.0 6.5 Control 4 E3795 40 × 140 81.5 93.6 7.7 Control 5 E3795 80 × 32582.6 93.9 7.7 Control 6 E3795 12 × 20 80.3 86.7 7.8 Control 7 E3795 80 ×325 79.0 86.0 8.5 Control 8 E3795 80 × 325 79.2 92.1 8.6 Control 9 E379540 × 140 80.2 88.1 16.6 Control 10 E3795 80 × 325 78.6 80.5 16.6 Control11 E3795 12 × 20 80.0 77.5 17.3 Control 12 E3505 80 × 325 80.3 72.6 21.0Control 13 F3860 80 × 325 80.0 65.5 26.5

Key to fiber material entries in Table 4:

“E1200” is EASTOFLEX polyalphaolefin from Eastman Chemical Co.

“E3505” is ESCORENE 3505 G isotactic polypropylene from Exxon ChemicalCo.

“E3795” is ESCORENE 3795 G isotactic polypropylene from Exxon ChemicalCo.

“E4023” is EXACT 4023 metallocene-catalyzed ethylene/butylene copolymerfrom Exxon Chemical Co.

Key to entries in Table 4, continued:

“F3860” is isotactic polypropylene from Fina Oil and Chemical.

“PUR440” is Morthane 440-200 polyurethane from Morton International.

“PUR455” is Morthane 455-200 polyurethane from Morton International.

The above data illustrates that particle-containing webs made fromadhesive fibers provided very good particle retention even at largeeffective fiber diameters. This can be better appreciated by plottingeffective fiber diameter against % particle retention, with theeffective fiber diameter on the abscissa and % particle retention on theordinate. The plot for Example Nos. 13-23 yielded a line having theequation:

 % particle retention=0.0447*(Effective Fiber Diameter)+96.70

The relatively flat slope of this line illustrated the insensitivity ofthe webs to particle loss at high effective fiber diameters. Incontrast, preparation of a similar plot for the webs made fromnon-adhesive fibers (Control Examples 2-13) yielded a line having theequation:

% particle retention=−1.151*(Effective Fiber Diameter)+98.78

The considerably more negative slope of this latter line illustrated thetendency of the control webs to undergo substantial particle loss atlarge effective fiber diameters.

EXAMPLES 24-25

Two particle-loaded webs were prepared as described in Example 1 exceptthe polyolefin was EASTOFLEX 1200 polyalphaolefin from Eastman ChemicalCo., the polypropylene was ESCORENE 3795 from Exxon Chemical Co. and thepolyolefin and polypropylene were combined in a 50:50 ratio. Both webswere loaded to a level of 90% with KURARAY TF 25×45 mesh carbon fromKuraray Chemical Co. The webs were evaluated for effective fiberdiameter, carbon retention using the shake test of Example 1, andpressure drop at a face velocity of 2 meters/second. The results are setout below in Table 5.

TABLE 5 Example 24 25 Basis Weight, g/m², particle- 485 439 containinglayer Effective fiber diameter, μm 22 35 % Particles retained in shaketest 91 87 Pressure drop, mm H₂O 21.3 8.0

The above data illustrates that the particle-containing layer exhibitedexcellent particle retention even at very large effective fiberdiameters, and low pressure drop even at high carbon loading levels.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention. It should be understood that this invention is notlimited to the illustrative embodiments set forth above.

What is claimed is:
 1. A method for making a respirator having anair-permeable sorbent-particle-containing layer and air-permeableparticle-retaining layers, at least one of the layers of such respiratorbeing a shape-retaining layer, comprising the steps of: a) forming suchparticle-containing layer from thermoplastic fibers and such particles,the fibers being sufficiently tacky after being formed by themselvesinto a particle-free web and cooled to room temperature so that the webwill adhere to itself; b) combining such particle-containing layer withthe particle-retaining layers so that the particle-containing layer isbetween the particle-retaining layers; and c) forming such layers to agenerally cup-like shape, wherein the particle-containing layer isstretchable during shaping to such cup-like shape without tearing orsignificant loss of particles.
 2. A method according to claim 1, whereinthe fibers of the particle-containing layer have an effective fiberdiameter less than about 10 micrometers.
 3. A method according to claim1, wherein the particle-containing layer, if shaken on a sieve shaker inthe presence of impact media, will retain at least about 90 weightpercent of the particles originally present in the web and the fibers ofthe particle-containing layer have an effective fiber diameter greaterthan about 10 micrometers.
 4. A method according to claim 1, wherein thefibers of the particle-containing layer comprise a stretchable blockcopolymer resin, an acrylate, a polyolefin or a polyurethane.
 5. Amethod according to claim 4, wherein the fibers of theparticle-containing layer comprise a polyalphaolefin, ametallocene-catalyzed polyolefin or a polyurethane.